1. Field of the Invention
The present invention relates to a recording/reproducing separated type head and an inductive magnetic thin film head for use in magnetic disk apparatuses.
2. Description of the Prior Art
Along with the capacity enlargement of magnetic disk apparatuses, the requirement for higher recording densities is increasing year after year. The apparatuses are required to be smaller and slower in circumferential speed. To meet these requirements, state-of-the-art magnetic disk apparatuses use a giant magnetoresistive (GMR) film, and their recording track width has been reduced less than 0.4 μm and their gap between the head and the recording medium (hereinafter referred to as the flying height), to 15 nm, both approximately.
FIG. 3 shows a perspective view of a recording/reproducing separated type head using a GMR head. The recording/reproducing separated type head has a structure in which an inductive magnetic thin film head for recording use is stacked over a GMR head exclusively for reproducing use. The recording/reproducing separated type head shown here is known as an upper shield/lower pole merged type, and an upper shield film 8 constituting the GMR head also serves as the lower pole of the inductive magnetic thin film head for recording use.
FIG. 4 shows a section of the upper shield/lower pole merged type recording/reproducing separated type head according to the prior art. Its reproducing GMR head comprises the upper shield film 8, a lower shield film 3, both for excluding all other magnetic fields than those of desired signals, a GMR film 5 for detecting desired signals, electrodes 6 for flowing currents to the GMR film 5, an upper gap film 7 and a lower gap film 4. On the other hand, the inductive magnetic thin film head for recording use comprises an upper pole 14 for generating a recording magnetic field, a coil 12 for applying a signal current and an interlayer insulator 13. These films constituting the heads are fabricated over a substrate 1 over which an insulating film 2 is stacked. Further, the whole head element is covered with a protective film 15.
In contrast to the upper shield/lower pole merged type recording/reproducing separated type head described above, an upper shield/lower pole separated type recording/reproducing separated type head is shown in FIG. 5. In this head, an insulating separation film 9 and a recording lower pole 10 are additionally formed over the upper shield film 8.
Unlike in the upper shield/lower pole merged type, as the recording magnetic field of the inductive magnetic thin film head is separated by the separation film 9 in the separated type head, it is difficult to impress the GMR head, which is an advantage to stabilizing the electric properties. However, there is also a disadvantage of complicating the manufacturing process.
The substrate 1 is usually a sintered product of A12O3 and TiC powder, whose surface has many fine pores (gaps). The insulating film 2 is intended to fill these gaps, which are filled by lapping A12O3 after coated it by sputtering. For the lower shield 3 and the upper shield film 8 constituting the reproducing GMR head, thin films of NiFe or some other alloy are used. The giant magnetoresistive (GMR) film 5 for detecting signals consist of very thin spin valve films stacked one over another, having a CoFe free layer. The upper gap film 7 and the lower gap film 4 usually consist of A12O3 thin films. The electrodes 6 consist of Ta layer which is hard on their sides exposed to the air bearing surface opposite the medium and, within the element, of Au, Cu and so forth, laminated to reduce the electric resistance.
On the other hand, the upper pole 14 constituting the inductive magnetic thin film head for recording use is made of a CoNiFe alloy thin film, which has a high saturation magnetic flux density and can generate a large recording magnetic field. The coil 12 for applying a recording current is made of Cu. The interlayer insulator 13 for insulating coils from each other or the coils from the upper pole 14 is made of a high molecular resin. The protective film 15 is made of an A12O3 film.
As noted above, the gap between the heads and the recording medium is increasingly narrowed with the rise in recording density. In order to achieve a high density of recording, the heads indispensably need to be lowered in flying height. However, along with the lowering of the flying height, the deformation of heads is posing an increasingly serious problem, because the deformation of heads would invite localized narrowing of the gap between the heads and the recording medium, and there would be a case that the heads and the recording medium would collide, which would in the worst case result in signal disappearance due to damaging of the recording medium or sliding of the heads. Studies on this problem include, for instance, what is reported in the IEEE Transaction on Magnetics, vol. 38, No. 1, JANUARY 2002, page 101. According to this article, heads are deformed by heating and, for example, warped immediately above the upper pole 14 as shown in FIG. 6 (deformed portion 20). As a consequence, the deformed portion 20 would become more liable to contact with the recording medium, and in the worst case the deformed portion 20 would be worn as shown in FIG. 7 (worn area 21).
Heads can be deformed by differences among their constituent layers in the ratio of expansion when the heads are heated. The heating of the heads in turn would be due to their ambient temperature or their own heat generation. Among the factors of ambient temperature, the temperature within the magnetic disk apparatus is dominant. Many magnetic disk apparatuses are guaranteed against a temperature of about 60° C. The self-generated heat of the heads mainly comes from the inductive magnetic thin film head, and its major factors include Joule heating due to the resistance of coils at the time of writing, eddy current heating in the high frequency region, iron loss and an increase in resistance by the skin effect.
To reduce the self-generated heat of heads, one of the first conceivable ways is to work on the source of heat. For instance, it would be effective to suppress Joule heating by reducing the resistance of coils.
At the same time, it is also effective to facilitate heat radiation and thereby make it difficult for the heads to generate heat. For example, a radiator plate may be provided near the source of heat to facilitate heat radiation and keep the head elements themselves from generating heat.
As described above, the self-generated heat of the heads mainly comes from the inductive magnetic thin film head. Therefore, an essential challenge is how to effectively radiate heat due to, for instance, the Joule heating of the coil 12 and the hysteresis heating of the upper pole 14 and the lower pole 10.
In order to ensure satisfactory heat radiation, it is desirable to arrange films having a high thermal conductivity near the sources of heat generation. Incidentally, the recording/reproducing separated type head is mounted over an A12O3 and TiC substrate having a large heat capacity and a high thermal conductivity. Thus the point is how to cause the substrate to radiate the heat generated by the inductive magnetic thin film head, and therefore how to bring the source of heat generation and the substrate close to each other poses an essential challenge.
As schematically shown in FIG. 4, in the current practice, the head element of the recording/reproducing separated type head and the substrate 1 are separated from each other by the insulating film 2, which may consist of A12O3 (alumina) for example. It has already been explained that this separation is intended to fill the pores (gaps) which are formed because the substrate 1 is made of a sintered product. Unless these gaps are filled with A12O3 (alumina), the magnetic properties of the magnetic thin films formed over them, such as the lower shield 3 and the GMR film 5, will become deteriorated, eventually with an adverse consequence on the electric properties and life of the head. The thickness of this insulating film 2 is usually a few μm or more. Furthermore, since the inductive magnetic thin film head is formed over a magnetoresistive head, it is formed around 10 μm away from the substrate 1 in the conventional recording/reproducing separated type head.
As described above, the heat generating portions of the inductive magnetic thin film head, including for instance the coil 12, are formed over a number of film layers, which obstruct heat radiation.